You might try the BPL search t http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/search? as this has been discussed many times— not that it isn't a good question.
The best I have seen so far is the Vibro Barefoot Ultra, although I have no idea what they are like on wet rock. The price isn't a casual choice category either. http://www.vivobarefoot.com/us/mens/ultra-mens?colour=Red
I would love to see a major shoe manufacturer really work on designing a wading and camp shoe for hikers, with weight, wet traction and retention (as in staying on your feet) being the major criteria.
The really light "slippers" are generally worthless and most sandals and water shoes would make a SUL aficionado cringe.
I saw some Crocs in a shop the other day that looked much like Keen sandals and of course I neglected to write down the model name. The *felt* light at any rate.
A number of cheap shoe marketing firms have made resin foam (like Crocs) "fisherman" style sandals that gave good foot protection and had some change of staying on while crossing a stream. The really cheap Croc knock-offs are another alternative, but I wouldn't trust them for stream crossing.
For plain old camp shoes, the lightest, cheapest flip flops would work for me, but I have hard time justifying the extra weight.
There are a number of uber-minimalist sandal designs that use thin rubber or plastic soles (or even insoles) with light cord. See http://xeroshoes.com/how-to-make-huaraches